Nicotinic Acid Catabolism Modulates Bacterial Mycophagy in Burkholderia gladioli Strain NGJ1.

Burkholderia gladioli strain NGJ1 exhibits mycophagous activity on a broad range of fungi, including Rhizoctonia solani, a devastating plant pathogen. Here, we demonstrate that the nicotinic acid (NA) catabolic pathway in NGJ1 is required for mycophagy. NGJ1 is auxotrophic to NA and it potentially senses R. solani as a NA source. Mutation in the and genes involved in NA catabolism renders defects in mycophagy and the mutant bacteria are unable to utilize R. solani extract as the sole nutrient source. As supplementation of NA, but not FA (fumaric acid, the end product of NA catabolism) restores the mycophagous ability of ΔΔ mutants, we anticipate that NA is not required as a carbon source for the bacterium during mycophagy. Notably, , a MarR-type of transcriptional regulator that functions as a negative regulator of the NA catabolic pathway is upregulated in Δ/Δ mutant and upon NA supplementation the expression is reduced to the basal level in both the mutants. The Δ mutant produces excessive biofilm and is completely defective in swimming motility. On the other hand, Δ/Δ mutants are compromised in swimming motility as well as biofilm formation, potentially due to the upregulation of . Our data suggest that a defect in NA catabolism alters the NA pool in the bacterium and upregulates which in turn suppresses bacterial motility as well as biofilm formation, leading to mycophagy defects. Mycophagy is an important trait through which certain bacteria forage over fungal mycelia and utilize fungal biomass as a nutrient source to thrive in hostile environments. The present study emphasizes that nicotinic acid (NA) is important for bacterial motility and biofilm formation during mycophagy by Burkholderia gladioli strain NGJ1. Defects in NA catabolism potentially alter the cellular NA pool, upregulate the expression of , a negative regulator of biofilm, and therefore suppress bacterial motility as well as biofilm formation, leading to mycophagy defects.